Method for testing bone conduction



Feb. 25, 1941. H FLETCH R 2,232,779

METHOD FOR TESTING BONE CONDUCTION Filed May 23, 1936 //v mv TOR V H. FL ETC/15R A TTORNE V Patented Feb. 25, 1941 UNITED STATES PATENT OFFICE Telephone Laborato York, N. Y., a corpora Application May 23,

1 Claim.

This invention relates to hearing tests and particularly to tests for measuring hard of hearing patients for a bone conduction receiver.

To determine the acuity of bone conduction in 5 the poor ear, it is necessary to mask the good ear in some manner to render it impervious to the action of the bone conduction receiver on the mastoid eminence adjacent the car under tests in order that the noise from the test will not reach the good ear either through the air or the osseous construction of the head.

The best method of masking the good ear against this condition is by the introduction of a tone into that ear which will provide the necessary masking effect and it has been determined that if this tone is a continuous one above the level of that applied to the bone conduction device and that of the bone conduction device is intermittent, the patient is able readily to distinguish what is perceptible in the poor ear.

The object of this invention is to provide a simple convenient apparatus by means of which the tests may be easily made in an efficient manner.

According to the general features of this invention a continuous tone is applied to the good ear of a patient through an air conduction receiver to mask that ear against an intermittent tone applied to a bone conduction receiver applied to the patient.

In the drawing which is a simple schematic of the apparatus and circuit for practicing this invention 5 designates a multiple frequency oscillator of well-known character provided with con- 35 ductors 6 and 1 leading to jack connections 8 to which an air conduction receiver 9 such as shown in W. C. Jones patent 1,668,910 may be connected by means of a plug l0. Included in this circuit is a network comprising series and shunt resistances II and I2 and a capacity 13 the purpose of which will be hereinafter described.

Connected to the opposite conductors 6 and 1 are conductors I 5 and I6 terminating in a jack ll adapted to receive a plug I8 connected with a bone conduction receiver 20 which may comprise a case 2| adapted to fit against the mastoid eminence of the patient and an electromagnetic vibrating system adapted to respond to the voice frequency currents to vibrate the mastoid eminence located within the case. A manually operries, Incorporated, New tion of New York 1936, Serial No. 81,404

ated key 25 located in the conductor 15 constitutes a means for interrupting the tone through the bone conduction receiver 20.

Inasmuch as the normal response characteristic of the air conduction receiver 9 is considerably 5 above that of known bone conduction receivers and the responses of the two devices may vary for different frequencies, the network comprising the resistances I l and I2 and the capacity I3 is inserted in the circuit in order to insure that the difierence in level of the two devices will be about thirty (30) decibles in favor of the air conduction device at any of the applied frequencies. It is important that the level between the response of the two receivers be maintained always the same since it insures that the car not being tested has sufficient sound in it to mask any sound produced by the bone conduction receiver.

It is also important that there be suflicient impedance in the circuit of the bone conduction re- 0 ceiver that the opening and closing of key 25 will not produce a flutter of sound in the air conduction receiver. This may be built into the bone conduction receiver or may be provided by means of a transformer 26 in the leads l5 and I6.

In the application of the apparatus for testing purposes the air conduction receiver 9 is placed in the good ear of the patient and the bone conduction receiver 20 against the mastoid eminence adjacent the poor ear. The tester adjusts the 30 oscillator for the frequencies and volumes desired and operates the interrupting key 25 until the patient signifies what his reaction is to the interrupted tone. From the results thus obtained the tester is able to prescribe a bone conduction 35 receiver of the best characteristics for the condition indicated by the patients response to the test.

What is claimed is:

The method of determining the bone conduction response in the hard of hearing which comprises applying by air conduction to the good ear of the patient a steady tone of given frequency and volume and by bone conduction to the osseous structure adjacent the poor ear an interrupted tone of the same frequency but of lower volume and noting the reaction of the patient to the interrupted tone.

HARVEY FLETCHER. I0 

